I'll be going to South America at the end of the summer. Not looking for any travel companions, but just some general comments:
Don't worry if you can't find anyone beforehand to travel with. When staying in hostels you'll meet so many other people that you will probably find various people to travel with, wherever you're going. I've been to Ecuador and Bolivia before, and I took a few weeks of language classes when I just arrived in Ecuador. Met quite a few other backpackers in my language school, and after that we traveled together trough Ecuador for 2 weeks, and some went to continue on traveling together to Peru afterwards.
Of course it's different for everyone, but I'd recommend being flexible and not scared to travel on your own for a bit, even (or especially) when you arrange to travel with people who are largely strangers to you. You might find out that you have other interests, other ways of traveling, that one has more money than the other, etc.. The good thing about traveling with someone you only vaguely know is that it is a lot easier to say "this isn't working" and go your different ways.
Good luck anyway!